The present invention relates in general to radio frequency devices and in particular to methods and devices for coupling radio frequency energy from transmission lines.
Until this invention, coaxial taps and couplers were installed by cutting and connectorizing RF cable using coaxial jumpers. The primary disadvantage of this methodology is the resulting excessive loss to the host cable. Stein et al, U.S. Pat. No. 5,729,184, subsequently taught that a tap can be used without connectorization; however, the Stein et al. invention still caused losses of over 1 dB to the host cable. Stein et al did mention the theoretical ability to devise taps with coupling losses up to 20 dB but did not describe a method for the manufacture of such devices.
What is needed are methods and devices embodying the ability to select the coupling loss and accompanying insertion loss in RF systems. In particular, such methods and devices should allow a wireless system not only to be tuned but should also allow minimization of the number of amplifiers and active devices required to RF illuminate a structure.
The present invention relates generally to a coupling device for obtaining energy from a transmission line. In one embodiment, the coupling device comprises a contact for contacting an inner conductor of the transmission line through an aperture in an outer conductor of the transmission line. At least a portion of the contact includes a coil of a preselected configuration, where the configuration defines at least one property of the transferred energy. The coupling device also includes a connector having an inner conductor coupled to the contact.
In another embodiment, the coupling device includes a wire of a preselected configuration positioned between the contact and the connector. The wire is spaced from a ground plane to create a selected parasitic capacitance and the configuration of the wire at least partially defines a center frequency of the coupling device.